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It’s not clear what’s causing the increased number of tick-borne diseases, but the trend doesn’t appear to be solely the result of better testing or greater awareness, said Bradley Tompkins, an infectious disease epidemiologist with the Vermont Health Department.
Health workers have already seen a record number of anaplasmosis cases, Tompkins said, and there are indications that pattern will continue through the fall.
Tick-borne illnesses will continue to be a concern at least through Thanksgiving, Tompkins said. While mosquito-borne illnesses are generally a problem only until the first hard frost, ticks don’t respond to seasonal weather in the same way, he said.
Anaplasmosis is spread by the blacklegged tick, the same species that transmits Lyme disease, babesiosis, Powassan virus and the bacteria Borrelia miyamotoi, which also cause disease.
In rare instances anaplasmosis may prove fatal. The most common symptoms are fever, malaise, muscle aches and headaches. Research in recent years by Lyndon State College faculty and state scientists suggests that about 7 percent to 10 percent of Vermont ticks carry the bacteria that cause it.
During those studies, ticks carrying anaplasmosis were found almost exclusively in the southern half of the state.
More than half the ticks tested across the state carried the bacteria responsible for Lyme disease. Ticks with this bacteria were found throughout the state.
The incidence of tick-borne diseases in Vermont has steadily increased since at least 2010, Tompkins said.
This rise can’t be explained by better testing methods, or by greater numbers of Vermonters alerting health professionals after they’ve been bitten, he said.
But it’s not clear what is driving the increase, he said.
Climate change is likely a contributing factor, but it’s hard to say to what degree, said Jared Ulmer, the climate and health program coordinator at the Vermont Department of Health.
Establishing links between climate change and certain ailments, such as heat illnesses, is a pretty straightforward task, Ulmer said. It’s much more difficult to find what relation exists between the Earth’s warming and things like Lyme disease, he said.
An example Tompkins related might illustrate why.
Research in New York has shown that trees like oak, walnut and beech undergo yearslong cycles of seed production, Tompkins said. Some years bring more nuts than others, he said.
Years with heavy nut production tend to encourage larger populations of white-footed mice in the following year, Tompkins said. This species of mouse is a particularly well-suited vector for Lyme disease, he said.
The year after these white-footed mice populations expand, Tompkins said, Lyme disease incidence in humans is typically greater than normal.
A number of other natural and artificial factors influence the prevalence of tick-borne illnesses, Tompkins said. Human development, for instance, creates good habitat for white-footed mice, he said.
Ticks also prefer warm, moist areas, he said. Research indicates that global temperature increases are likely to bring both these conditions to New England, Ulmer said.
White-footed mice, shrews and Eastern chipmunks are all known “reservoirs” for tick-borne diseases, Tompkins said. This is in part because these animals don’t mount an immune response to the Lyme disease bacteria, he said, which allows the bacteria to thrive as long as their host survives.
Ticks born in the spring typically feed on small mammals that spring or summer, and over the following year they mature into nymphs, Tompkins said. These nymphs typically feed again — this time on a variety of animals, including humans — the spring or summer following their first birthday.
Adult female ticks often feed again in the fall, as do a few nymphs and males, in preparation for the winter, Tompkins said.
This fall “blood meal” is the one Vermont authorities are concerned could break records again this year, he said.
The high number of anaplasmosis cases Vermont health workers encountered this summer is an early indication that high numbers of tick-borne diseases are likely in the fall, Tompkins said.
It’s important to note that the most common tick-borne disease, Lyme disease, is curable, he said.
A popular misconception exists that people who contract Lyme disease will carry it for the remainder of their lives, he said.
“That’s simply not true,” Tompkins said.
Existing antibiotics can cure Lyme disease, he said, although some of the effects of the disease may linger for months afterward.
Nevertheless, Tompkins said, early treatment is important, as this reduces the likelihood of lingering symptoms.
Vermonters bitten by ticks can contribute to a state database at a Health Department tick tracker, found here.
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